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Synergic effects of laser – TIG welding
Kubíček, J. ; Doležal, P. ; Mrňa, Libor ; Šebestová, Hana ; Horník, Petr
Laser welding compared to conventional arc methods is accompanied by rapid cooling rates. It can lead to the formation of undesirable microstructure of the weld metal and heat affected zone of some steel grades which has a negative impact on their mechanical properties. The preheating is quite problematic because of high speed of laser welding. The possibility of preheating by the heat of the arc discharge of the associated TIG burner has been tested. Precise holder has been fabricated to fix the burner to the laser welding head allowing TIG electrode positioning towards the laser beam and the workpiece. A number of high strength steel S460MC and S700MC welding experiments was performed. The effect of TIG current on microstructural changes has been proven. Some welding experiments were compared to the SYSWELD welding simulations.\n
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Assessment of weld defects during laser welding with beam wobbling of aluminum alloy
Slíž, Michal ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
This bachelor thesis is aimed on assessment of weld defects during laser welding with beam wobbling of aluminum alloy. Theoretical part deals with study of main types of industrial lasers, laser modes and analysis of beam wobbling technique. Further described aluminum alloys, their weldability, weld defects and methods of their evaluation. In the experimental part, sixteen test welds are made on sheet metal from aluminum alloy AlMg3. This is followed by the evaluation of the defects and determination of optimal welding parameters.
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Study of properties of laser welds of Domex 700 MC material using arc preheating
Kosinka, Jakub ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
This thesis deals with the study of influence of preheating/reheating by TIG arc method in the laser welding process of Domex 700 MC fine-grained steel through the evaluation of laser-welds properties, respectively properties of welds made by laser-TIG hybrid technology. The main part of this thesis is experiment, in which Domex 700 MC plates 3 mm thick were welded – first using laser itself, then using laser with arc preheating and finally using laser with arc reheating. The variable parameter during the processes preheating or reheating was distance of TIG tungsten electrode and laser beam (DLA = 1 mm, 2 mm and 4 mm). The criterion for the assessment of welds properties thus produced was tensile strength verified by the tensile test. For a more detailed study of the laser-welds properties, a macrostructure / weld microstructure analysis and a Vickers hardness test were performed.
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Properties of hybrid LasTIG welds of of S460MC steel
Šebestová, Hana ; Horník, Petr ; Mrňa, Libor
Modern structural high strength low alloy steels achieve their excellent strength properties through the microalloying and carefully controlled process of hot rolling. Welding technologies with low heat input are advisable to maintain fine-grained structure of these steels and to minimize heat distortions. Laser beam is a source of highly concentrated energy and thus very narrow heat affected zone is reached during laser welding. Unfortunately, undesirable quenching microstructures can be generated thanks to high heating and cooling rates in both weld metal and heat affected zone. Their amount can be reduced through the temperature rate decrease realized using preheating. Technology of LasTIG hybrid welding combines laser welding with the preheating by an electric arc. The contribution evaluates the effect of electric current on LasTIG weld macro and microstructure and microhardness.
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Advanced laser welding methods
Mrňa, Libor ; Horník, Petr ; Šebestová, Hana
Recently, modern methods of laser welding have been developed. Laser welding methods employing scanning techniques are used. The basis of scanner laser welding is a laser head including system of two computer-controlled deflecting mirrors, supplemented with special optics, allowing fast beam movement over a given area. The second method using deflecting mirrors is wobbling welding. In this method, besides the main movement, laser beam oscillates along the welding trajectory. Weld seam width and microstructure can be varied by controlling of parameters of beam micro-motion.\nAnother advanced method is hybrid laser-TIG welding where arc discharge can serve as a heat source regulating heating or cooling rate. This method can be used for high strength fine-grained steels welding, where the additional heat affects the weld microstructure and the heat affected area and consequently improves mechanical properties of the weld joint.\n
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Hybrid welding of high-strength steels
Horník, Petr ; Šebestová, Hana ; Mrňa, Libor
High-strength steels represent a significant group of materials in the field of automobile construction, agricultural and construction machinery, mining conveyors or bridge construction. The excellent strength characteristics is achieved due to the very fine-grained structure ensured by microalloying and the controlled rolling process. In order to preserve the fine-grained structure and hence the required properties and minimize thermal distortions, it is advisable to use welding technologies that do not bring excessive heat to the material. At the same time, however, it is advisable to avoid large temperature gradients that support the formation of fragile microstructures. Therefore, an electric arc preheating is placed before the laser beam and its influence on the weld geometry and the heat-affected area is evaluated.\n
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The Emotional inteligence of pre-school children
ŠEBESTOVÁ, Hana
The thesis deals with the emotional intelligence and the emotional development of preeschool children. The theoretical part is focused on the definition of the terms children's emotional intelligence, emotions, emotional difficulties and also on possibilities of the emotional intelligence development. The aim of the practical part is to encourage the emotional intelligence development and to catch the process of realization in a group of children. This is complemented by a case history. The study is carried out with qualitative method by way of dialogue and involved observation. The conclusion of the thesis describes the project's realization progress and it finds out the utility of applied techniques from the point of view of the emotional intelligence development support.
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Evaluation of Company Performance
Šebestová, Hana ; Bejčková, Zdeňka (referee) ; Režňáková, Mária (advisor)
This thesis deals with the evaluation of performance and financial health of the company Avanta Systeme from 2006 to 2010. Based on its financial and strategic analyses and a comparison of its results with two competing companies and average values in the respective branch of industry, suggestions to improve the firm's situation are presented.
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Mechanical properties of optical thin films
Tomáštík, J. ; Čtvrtlík, R. ; Šebestová, Hana ; Schovánek, Petr ; Jankůj, J. ; Hrabovský, Miroslav
Mechanical properties of optical thin films and coatings are very important for their reliability, because they are often exposed to rough conditions in service. Mechanical attributes of films, that determine their behavior, are in the center of interest. In this paper, mechanical properties of optical thin films deposited on various types of glass substrates were examined. Assessment of such properties was performed using instrumented nanoindentation (hardness, elastic modulus, elastic and plastic work done by indentation) and scratch test (critical loads corresponding to the onset of specific failure). The failure modes of thin films were discussed.
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